1. Field of the Invention
This invention relates to pipe cutting mechanisms and more particularly to a mechanism for cutting pipe from the inside thereof.
2. Description of the Prior Art
Tools for cutting pipe, tubing, conduit and the like are well known in the art with many such devices having been devised for particular applications, particular pipe material and for particular ranges of pipe diameters.
Normally, pipes are cut from the outside with a cutting tool which is rotated therearound to produce an ever deepending circular cut until the pipe is severed. In many applications, the external type of pipe cutter is entirely satisfactory, however, oftentimes it is impractical or otherwise undesirable to employ this type of mechanism.
By way of example, cutting the pipe from the outside can be impractical on a construction site when the pipe has been installed in a floor, ceiling or wall structure. In such installations when an error occurs, such as pipe or fixture misalignment, or other dimensional errors, it is often necessary to cut the pipe flush or below the surface of the structure in which the pipe has been previously installed so that corrective measures can be taken. To employ an external pipe cutter under circumstances of this nature would require dismantling of some types of structures such as wood, and the destruction of portions of such structures as wall board and concrete to provide sufficient room for rotation of the cutting mechanism.
Internal pipe cutting devices have been devised for use in situations such as that described above, however, several problems exist which have hampered the development and commercial acceptance of such mechanisms.
One such problem arises from the materials of which the pipe is fabricated. If the pipe is made of a hard material, such as asbestos-cement, considerble forces are exerted during the cutting operation, and accurately made rigid supporting mechanisms are needed to withstand such forces. Therefore, many prior art mechanisms have been very bulky and expensive.
Another problem which has kept many prior art devices from achieving commercial acceptance is the various sizes of pipe which need to be cut from the inside. Several adjustable devices have been devised to cut pipe of various diameters and various wall thicknesses. Due to such factors as cutter blade travel, the need for supporting the cutter mechanism relative to the bore of pipe, and the cutting forces exerted, tools which can be adjusted to cut various sizes of pipe are inherently complex, expensive and bulky. This may be more easily seen upon consideration of the factor of cutter blade travel. In general, such devices employ a plurality of cutter assemblies, made up of cutter wheels and suitable carriages, which are radially extendable, by means of a suitable expander mechanism, into engagement with the bore of the pipe. Thus, to cut a pipe having a relatively large inside diameter with a tool that can also fit into and cut a pipe having a relatively small inside diameter requires that the cutter assemblies be capable of moving a considerable distance. Therefore, the cutter assembly supporting and guiding structures must be capable of accommodating the required amount of travel, the expander mechanism must be capable of producing the needed travel and the entire tool must have sufficient structural strength to be able to withstand the forces exerted. An additional consideration is that the cutter assemblies must not be allowed to have excessive amounts of deflection or an uneven or jagged cut results. The problem of supporting the cutter assemblies to prevent deflection thereof becomes more complex when the assemblies are required to travel large distances.
A typical type of prior art mechanism for cutting pipe from the inside includes three cutting assemblies each having a cutting wheel or blade mounted on a suitable carriage. The cutter assemblies are carried in equally spaced radial increments within a cutting head. A cone shaped expanding mechanism is positioned between the inwardly disposed ends of the cutter assemblies, and the assemblies will radially extend and retract in response to movements of the cone therebetween. An example of this type of mechanism may be seen in U.S. Pat. No. 442,125 issued to F. Levasseur on Dec. 9, 1890. This mechanism, and others of similar structure, require that a relatively large cutter head be employed to accommodate the three cutting assemblies and the cone which spaces the cutter assemblies apart in their retracted positions. Thus, this type of prior art structure is limited to use on pipes having a relatively large inside diameter.
In view of the above, it may be seen that prior art cutting tools are comparatively complex, bulky, and in some instances expensive mechanisms with the bulk factor being of considerable importance as it prohibits the use of such tools in relatively small pipe.
Therefore, a need exists for a new and useful tool for cutting pipe from the inside which eliminates some of the problems of the prior art.